Insights of Active Extension Within a Collisional Orogen From GNSS (Central Betic Cordillera, S Spain)

Abstract

The coexistence of shortening and extensional tectonic regimes is a common feature in orogenic belts. The westernmost end of the Western Mediterranean is an area undergoing shortening related to the 5 mm/yr NNW‒SSE convergence of the Nubia and Eurasia Plates. In this region, the Central Betic Cordillera shows a regional ENE‒WSW extension. Here, we present GNSS‐derived geodetic data along a 170 km‐long transect orthogonal to the main active normal faults of the Central Betic Cordillera. Our data indicate that the total extension rate along the Central Betic Cordillera is 2.0 ± 0.3 mm/yr. Extension is accommodated in the eastern (0.8 ± 0.3 mm/yr in the Guadix‐Baza Basin) and western (1.3 ± 0.3 mm/yr in the Granada Basin) parts of the Central Betic Cordillera, while no extension is recorded in the central part of the study area. Moreover, our data permit us to quantify, for the first time, short‐term fault slip rates of the Granada Fault System, which is one of the main seismogenic sources of the Iberian Peninsula. We deduce a fault slip rate of ∼1.3 ± 0.3 mm/yr for the whole Granada Basin, with 0.9 ± 0.3 mm/yr being accommodated in the Granada Fault System and 0.4 ± 0.3 mm/yr being accommodated in the southwestern sector of the Granada Basin, where no active faults have been previously described at the surface. The heterogeneous extension in the Central Betic Cordillera could be accommodated by shallow high‐angle normal faults that merge with a detachment at depth. Part of the active extension could be derived from gravitational instability because of underlying over‐thickened crust.

Active Shortening Simultaneous to Normal Faulting Based on GNSS, Geophysical, and Geological Data: The Seismogenic Ventas de Zafarraya Fault (Betic Cordillera, Southern Spain)

“…This front is also consistent with the data published by Martín‐Rojas et al. (2023), suggesting a compression of up to 0.6 mm/yr.…”

“…The GNSS data show a general displacement to the W–SW with respect to stable Iberia (Figure 1b) and ENE–WSW shortening (Galindo‐Zaldívar et al., 2015; Martín‐Rojas et al., 2023), consistent with geological evidence of compression at the western and southwestern boundaries of the Granada Basin. Seismological data west of the Granada Basin differ providing earthquake focal mechanisms (EFMs) not only of compressional faulting, but also of strike‐slip and normal faulting.…”

“…While the Granada Basin is characterized by extensional structures (Galindo‐Zaldívar et al., 2015; Madarieta‐Txurruka et al., 2021; Martín‐Rojas et al., 2023), the tectonic activity to the west is more heterogeneous (Figure 2). From south to north, the activity changes as follows: (a) in the Internal Zones, to the south, there is no significant crustal seismicity, although the current development of Sierra Tejeda (Ruano et al., 2004) suggests NE–SW compression, (b) the central sector (Figure 5) is characterized by a NNE–SSW shortening observed by the Zafarraya GNSS network, and (c) the western sector, around Sierra Gorda, is more complicated (Figure 2), being affected by recurrent seismicity limited to the north by a dextral discontinuity (EFM in Figure 3) (Iznájar 1998 sequence; Stich et al., 2003).…”

“…The Betic Cordillera is currently affected by a NNW–SSE to NW–SE 4–6 mm/yr Eurasia‐Nubia convergence (DeMets et al., 2010; McClusky et al., 2003; Nocquet & Calais, 2003). At the same time, a nearly 2 mm/yr ENE–WSW extension perpendicular to regional compression occurs in the central Betic Cordillera (Galindo‐Zaldívar et al., 2015; Martín‐Rojas et al., 2023; Palano et al., 2015; Serpelloni et al., 2007), forming active high‐ and low‐angle normal faults (Galindo‐Zaldívar et al., 1999; Lozano et al., 2022; Madarieta‐Txurruka et al., 2021, 2022; Sanz de Galdeano et al., 2003). Today, the Granada Basin is the main extensional active basin of the central Betic Cordillera (Morales et al., 1990; Rodríguez‐Fernández & Sanz de Galdeano, 2006).…”